This is my ninth such ranking for Insider, and this time around there's a ton of turnover on the list thanks to the big year for rookies in 2015. In fact, my No. 1 and No. 3 prospects from last year won the Rookie of the Year awards in the NL and AL, respectively, and the Nos. 6 and 15 prospects were the runners-up in the AL. Eleven of my top 20 prospects last year graduated to the majors.

As usual, the list is heavy on position players up the middle, with a fifth of the top 100 currently playing shortstop. And there's a slew of center fielders on the list, but it's very light on catchers and third basemen. There also is a bit of a renaissance for left-handed starters right now, with a dozen on the list this year. The back of the list seems, just at a glance, to be the youngest I've had in years, thanks in part to all the graduations from the high minors in the past year.

The guidelines

The rankings are limited to players who still have rookie eligibility; that means they have yet to exceed 130 at-bats or 50 innings pitched in the majors and have not yet spent 45 days on the active roster of a major league club, excluding call-ups during the roster expansion period after Sept. 1.

Only players who have signed professional contracts are eligible.

I do not consider players with professional experience in Japan or Korea "prospects" for the purpose of this exercise. I also exclude Cuban players who are considered professional free agents by Major League Baseball by virtue of their experience in Cuba's Serie Nacional de Béisbol. As such, this list excludes Byung-Ho Park and Kenta Maeda, but it will consider Cuban players whom MLB treats as amateurs, like Yusniel Diaz (who is in the rankings) and Yadier Alvarez.

When ranking players, I consider scouting reports on players -- usually my own, supplemented with conversations with other scouts and front-office executives, as needed -- as well as performance, adjusted for age and context. I've made one adjustment in my ranking philosophy in recent years, favoring higher-upside prospects over lower-ceiling prospects that are closer to the majors. This better reflects how these players are valued now by front offices and scouting departments, and it gives me a chance to deliver more information on prospects whose names or scouting reports might be new to you.

I use the 20 to 80 grading scale in these comments to avoid saying "average" and "above average" thousands of times across the 100 player comments. On that scale, a grade of 50 equals major league average, 55 is above average, 60 is plus, 45 is fringy or below average and so on. Giancarlo Stanton has 80 raw power, for instance. David Ortiz has 20 speed. Andrelton Simmons is an 80 defender with an 80 arm. An average fastball for a right-hander is 90 to 92 mph, with 1 to 2 mph off that for a lefty.

I've included last year's rank for players who appeared in the Top 100 in 2015. An ineligible player (labeled as "NE" for not eligible in the 2015 rank area) was still an amateur at this time last January, whereas an unranked player (labeled "NR" for not ranked) was eligible but didn't make the cut. I've also tagged players who were on last year's sleepers lists ("SL") -- I listed a player or two per team in my 2015 team-by-team prospect rankings -- and identified those on my list of 10 players who just missed the cut ("JM").

Seager is the game's best prospect, a superlative hitter who projects to do everything at the plate and might even be able to do it at shortstop for a year or two before becoming a top-flight defender at third base.

Seager, the younger brother of Mariners third baseman Kyle, has electric hands at the plate and does everything very easily -- his swing, hip rotation and power look effortless -- but it's his approach that makes him the best prospect in baseball. Seager's pitch recognition is advanced way beyond his years, and you'll see him make adjustments within at-bats that even veterans don't make. He's better than most players his age at adjusting to a pitch he didn't expect and does very well covering the outer half without creating a hole on the inner third. He's tall and his swing plane can be high, so he's a little vulnerable to the pitch down at the knees. But for someone his age, that's a minor weakness to have as your primary issue at the plate.

While Seager reached the majors as a shortstop, he's already one of the biggest players in major league history to man that position and is likely to outgrow it if he hasn't already done so. (Seager is listed at 215 pounds; the only heavier shortstops in MLB history have been Hanley Ramirez, late-in-his-career Miguel Tejada, Juan Uribe and Alex Rodriguez.) Seager has the hands for short but not the speed or agility, while his arm would play anywhere on the diamond, making a move to third base -- where his defense would likely be plus or better, perhaps saving as many as 10 runs per year -- the most probable long-term outcome. He has MVP upside even if he moves to third, and would be even more valuable if he beats my expectations and hangs around at short.

Older brother Kyle, still just 28, already has had four All-Star-caliber seasons for Seattle, but he's going to end up second fiddle to his big little brother.

Insider

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